Introduction

Spark is a new email client by Readdle, makers of great “work-on-iOS-enabling” apps like PDF Expert 5 (Review), Scanner Pro, Documents, and more.
Their main focus is to make you "like your email again"; the 18 months of work have been worth the effort. With great third-party integration like Dropbox, Evernote, or Google Drive, and tiny details like enabling you to glance at your Calendar and Quick Replies, you'll be able to act on your emails much faster and easier – all without ever leaving the app.

First steps

After a short introduction you can add you email account from one of the common providers like iCloud, Google, Outlook, Exchange, and others. To make this process easier, Spark supports 1Password integration so your information is just a tap away. Just after checking your account you have your first encounter with a great new feature called "Smart Notification". It works similar to Apple's VIP Settings with the big difference that you don't have to move those contacts around and especially not give them VIP privilege for everything, just email notifications.
You can now start using your new email client as it comes, or edit the user interface and add some settings to make it work better for your needs.

UI

You can personalize the sidebar, change the swipes, and customize the widgets. For now there is a limited amount of "cards" you can use to customize your interface, with more coming in the future. Cards are intelligent filters that - depending on the content - sort your emails for you and lets you process them much faster. You can then either add them to your Sidebar, or have your most used as Widgets.

Widgets can be customized in two different ways: On Top, which gives you on tap access to your cards, or at the bottom, which adds a new icon next to the compose icon and also changes the top bar to a slider which lets you quickly jump between your Smart Inbox and the unified Inbox (normally accessed via Sidebar). Depending on your needs, this can already be on big step up the productivity ladder.

Talking about productivity, you can tweak your Settings in the UI section to let you achieve "Inbox Zero" if your change the Email Flow to "Move to Archive" when you've read them, and change the Badges count to "Whole Inbox".
Your Swipe gestures are also customizable as seen in the images above, and the Move and Snooze gestures can be really handy when pursuing an action based email-strategy. The Snooze function is particularly handy as the only way of triggering it otherwise is to pin the email first and then hit the watch icon in the top right (as pictured below). Every snoozed email will then be moved out of your Inbox and can be found either in the "Snoozed Pins" card or in a folder created by Readdle.

Features

Another useful feature is Smart Search that enables you to search your Inbox using natural language and exact terms like "Attachments from Sabrina" or "Beta last two weeks" which you can also save if you use them regularly.
The aforementioned Smart Notification and Smart Inbox are handled by the app itself and categorize your incoming email depending on the sender and its importance. There is a way to change that behavior for future emails by tapping on the sender where you can edit some of the details. The bell lets you change the smart notification while the message type lets you change the section you'll find the email in the next time you get one.

Handling Email

A lot of effort has been put into handling your email. Email is still one of the most used methods for professional work. Unfortunately many people don't get the importance of it and use it in ways that could be dealt with differently. You're then trapped between reading hundreds of emails to find the ones that are important, declaring email bankruptcy and deleting the all or having your inbox overflow with them, or you spend many useless hours going through them while you could have spent that time in a different way. Either you're receiving or answering email, managing them can be a real hassle. That's where Spark really shines.

Receiving Emails

Besides having the Smart Notifications and Inbox take a lot of pressure from you, there is one very special feature that will save you hours, Quick Reply. We're starting to get accustomed to sending quick replies with the Apple Watch and while you can do so with Spark on the Apple Apple Watch as well, there's a great way to let the recipient know what you think about their email in Spark.
As pictured below, these quick replies are the perfect way of letting someone know what you think about their message without wasting too much time and being too hard on them. A simple thank you, a smile, or a like is just a tap away and you're done. Presented in a nice way, the recipient will appreciate the (non-existent) effort.

As mentioned before, pinning and snoozing emails that are important is just a tap or a swipe away, and there's also the possibility to export it as a PDF to one of many services like Dropbox, iCloud Drive, Google Drive, Evernote, and others. If you're subscribed to interesting newsletters or get links from a friend or colleague, you can even send them to Instapaper, Pocket, Evernote, Readability, or OneNote. Besides these integrated services you can of course trigger the iOS Share Sheet for your personal apps.

Your Smart Inbox enables you to see your emails categorized in different sections which you can process even faster. Either by tapping on the checkmark for each category you can mark them all as read, or when tapping on the category itself you can slide the bottom bar to act on these email after having glanced at them first.

Sending Emails

Sending emails presents the same problems as receiving them. We tend to spend too much time with it, fiddling around with little things that could be done in seconds, but usually end up taking minutes including jumping around between apps.
The clean interface lets you add the recipient with the possibility to and a copy or blind copy just by typing Cc: and Bcc:. Really handy integration without additional, often unused bulk.

A really clever integration is the way of handling signatures. After your first draft the app analyzes your previous emails to determine your most used signatures and creates them for you. To change your signature just swipe until you get the one you like or none at all.
As for attachments, you can use the obvious Camera and Albums or use of the previously mentioned services. While it's convenient to be able to get any file from your iCloud Drive of Dropbox, I'm missing the ability to generate and copy a link to a bigger file in your Dropbox.
When you need a file someone sent you, you can minimize the draft to look for the attachment, long press the the file and tap attach to directly add it to your draft. This can also come in handy when you need to check you calendar real quick for availability.

Details

One thing that was a joy to see from the beginning was the integration of 1Password. If you offer the choice of different third-party services, there's no easier way of doing it. Something I found interesting though was the way Spark handled the logins. Dropbox for example didn't open the app for authorization, instead it opened a browser window inside the app and let me type in my credentials which was no hassle with 1Password. Instapaper and Evernote did the same, while Pocket directed me to the app to ask for permission.
You can edit what the categories show in your Smart Inbox through long pressing on them. How many visible items you have, if they're unified, or if you want to have an overview per account.

In Calendars view you can add an event through long pressing on the desired time. When creating a new event you get the generic Apple Calendar event creation sheet. No natural language available here. On one side it's funny as it's used for search and also in their Calendars 5 app, but understandable though. If you need more functionality go to your app of choice, this here is just for quick reference.

There could also be more integration with Readdle's own apps, but that would as well defy the purpose of the email app itself. There's always the possibility to work in another app and invoke Spark via Share Sheet.

While I don't battle with several hundreds of emails on a daily basis, I'm really happy with the way Spark is handling my Inbox. For me it's the perfect balance between being an easy and fast way to reply and go through my important emails, while also being powerful enough to let me act on and share the details that need more attention.

Spark is the first email client to replace Apple's Mail app on my home screen. Not because others weren't good enough, but primarily because I never cared enough to process emails on my iPhone.

The video below will show you how easy and fast you'll get through your Inbox in the future, and with the Apple Watch you'll be notified about the emails that are important besides your VIPs.

Spark will help you "like your email again", and is available on the App Store for Free with more cards coming in future.